A Copernican eye-opener

Copernicus: A Very Short Introduction

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Approximately 500 years ago a Polish lawyer, medical doctor, and churchman got a radical idea: that the earth was not fixed solidly in the middle of all space, but was spinning at a thousand miles per hour at its equator, and was speeding around the sun at a dizzying rate. Unbelievable, critics said. If that were true, at the equator people would be spun off into space. And it would be much harder to walk west than east.

Copernicus’ book, On The Revolutions of the Heavenly Spheres, was finally printed in 1543, the last year of his life. Few people got upset by its world-shaking proposal, to fix the sun in the middle of a planetary system. It was too technical for common folk to understand, and the specialists regarded it as a recipe book: how to calculate the positions of the stars and planets, but not a description of physical reality. Nearly a century and a half would pass before a majority of educated people would accept that the earth was really spinning around the sun.

But writing a Very Short Introduction to Nicholas Copernicus posed a serious dilemma: how not to trivialize the monumental move from geocentric to heliocentric on the one hand, or get bogged down on the computational details that fill his book on the other. For example, an important part of his On The Revolutions shows how to use a minimum number of carefully chosen observations to set up the tables for finding the positions of the planets at any time of the past or future. Not the stuff for casual reading or philosophical posturing.

And then a solution occurred to me: I could chose a single example of a long calculation and put it in an appendix. There any reader who wanted an idea about the calculations could take a peek without getting totally involved. For my example I chose the position of Mars in the sky on February 19, 1473, which happens to be Copernicus’ birth day. What happened next was a real eye-opener. I had made similar calculations before, and figured I would have the copy for the printer in about three days. Instead, it took nearly a month.

Finding some of the numbers buried in the text (rather than in a neat table) was not so easy. Precisely how Copernicus was treating the so-called precession was another stumbling block. Choosing which of very similar (but modestly different) tables was like a poorly marked detour. And one critical key number he did not give at all, as if he had forgotten a required table. In thinking about this situation, I realized that from the book’s publication in 1543 through to 1550, there was only a single volume of planetary positions based on Copernicus’ numbers, authored by the Polish astronomer’s only student. Not until 1551, with the publication of a revised set of Copernican numbers, did his planetary positions take their stand in the astronomical marketplace.

Georg Joachim Rheticus, Copernicus’ only student, had had to work very hard to persuade the Polish master to allow his book to be published. Now we can only wonder: was Copernicus so reluctant to publish because he knew that his book was not really finished? Copernicus’ De Revolutionibus was not for everyone — it was of course in Latin and too technical for those who hadn’t been to a university. There’s a very amusing section in Robert Recorde’s popular astronomy book of 1556, where the Master mentions Copernicus, “a man of greate learninge, of much experience, and of wonderful diligence in observation.” To which the Scholar replies, “Nay syr in good faith, I desire not to heare such vain phantasies, so far againste common reason and repugnante to the consente of all the learned multitude of Wryters, and therefore let it passe for ever, and a daye longer.”

But the Master has the last word: “You are too younge to be a good judge is so great a matter: it passeth farre your learninge and theirs also that are much better learned then you, to improve his supposition by good argumentes, and therefore you were best to condemne no thing that you do not well understand.” It was in the next century that Isaac Newton’s picture of gravity showed why people at the equator would not be spun off into space by the spinning earth, and if there were any doubts left, the successful predicted return of Halley’s comet in 1759 clinched the basic picture of the Copernican system. Despite his reservations about the last chapters of his book, Copernicus would have been both surprised and pleased that if his heliocentric system didn’t give a final blueprint for the solar system, at least the sketch was recognizably correct.

Featured image credit: Sun Planet Solar System by Valera268268. Public domain via Pixabay.

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Recent Comments

I realize this is spitting into the wind, but Copernicus’ ethnic origin has been mistaken for centuries. He came from a town Kopernik whose name is Old Prussian, not Polish, on the border between Poland and the Teutonic Order’s Prussia. His enrollment entry at University was Prussian, not Polish. Prussians (a Baltic tribe) were conquered by the Order and eventually were assimilated by the German settlers–except for those living across the border in Poland. Eventually they assimilated as Poles. But in Copernicus’ time they and their language still survived, and it seems that Copernicus himself was an ethnic Prussian, not a Pole. (Remember, those Prussians were not Germanic, but Baltic.)

Easwar21st August 2016

The notion that the Earth revolves around the Sun had been around as early 3rd century BC by Aristarchus of Samos. But the earliest idea that it is the Earth that is actually moving, with the Sun at the centre (Heliocentrism) is found in several Hindu Vedic Sanskrit texts written in ancient India.
The Hindu sage Yajnavalkya (c. 9th– 8th century BC) recognized that the Earth is spherical and believed that the Sun was “the centre of the spheres” as described in the Vedas at the time. In his astronomical text Shatapatha Brahmana (8.7.3.10) he states: “The sun strings these worlds – the earth, the planets, the atmosphere – to himself on a thread.” He recognized that the Sun was much larger than the Earth, which would have influenced this early heliocentric concept. He also accurately measured the relative distances of the Sun and the Moon from the Earth as 108 times the diameters of these heavenly bodies, close to the modern measurements of 107.6 for the Sun and 110.6 for the Moon.
The Vedic Sanskrit text Aitareya Brahmana (2.7) (c. 9th–8th century BC) also states: “The Sun never sets nor rises thats right. When people think the sun is setting, it is not so; they are mistaken.” This indicates that the Sun is stationary (hence the Earth is moving around it), which is elaborated in a later commentary Vishnu Purana (2.8) (c. 1st century), which states: “The sun is stationed for all time, in the middle of the day. […] Of the sun, which is always in one and the same place, there is neither setting nor rising.”
The Hindu philosopher Aryabhata (476–550), in his magnum opus Aryabhatiya (499), propounded a planetary model in which the Earth was taken to be spinning on its axis and the periods of the planets were given with respect to the Sun. He accurately calculated many astronomical constants, such as the periods of the planets, times of the solar and lunar eclipses, and the instantaneous motion of the Moon.